Accurate measurements of cellular mechanical properties are critical to understand a cell's biological response to its environment. The quality of mechanical measurements depends greatly on the attachment method of the apparatus to the cell specimen. Attachment methods for single-cell specimens are much more tedious than those used on multi-cell specimens. There are no available external attachment locations forcing the apparatus to attach directly to the cell membrane. Therefore, the attachment method must not disturb the specimen while still providing strong enough attachment strength to allow for the application of large forces to the specimen. There have been a number of proposed attachment methods including wrapping, glass micro-needles, and suction micropipettes. Reference is made to the following: Fabiato, A., and F. Fabiato, 1975, “Contractions Induced by a Calcium-Triggered Release of Calcium From the Sarcoplasmic Reticulum of Single Skinned Cardiac Cells . . . . ” The Journal of Physiology 249 (3) (August): 469-495; Iribe, Gentaro, Michiel Helmes, and Peter Kohl. 2006, “Force-Length Relations in Isolated Intact Cardiomyocytes Subjected to Dynamic Changes in Mechanical Load . . . . ” American Journal of Physiology. Heart and Circulatory Physiology 292 (3) (March): H1487-97, doi:10.1152/ajpheart.00909.2006; Tajitsu, Y. 2008 “Piezoelectricity of Chiral Polymeric Fiber and Its Application in Biomedical Engineering” IEEE Transactions on Ultrasonicsm, Ferroelectronics, and Frequency Control 55 (5) (May): 1000-1008. doi 10.1109/TUFFC.2008.746; Brady, A. J., 1991, “Mechanical Properties of Isolated Cardiac Myocytes . . . . ” Physiological Reviews 71 (2) (April): 413-428; Prosser, Benjamin L., Christopher W. Ward, and W. J. Lederer, 2011, “X-ROS Signaling: Rapid Mechano-Chemo Transduction in Heart . . . . ” Science (New York, N.Y.) 333 (6048) (September 9): 1440-1445, doi:10.1126/science.1202768; Krulevitch et al.; Cohen, A. L., “Medical Devices and EFAB Methods and Apparatus for Producing Them” 2005; Publication No. US2005/0121411; as well as United State Patent Publication US 2012/0096955 of Guth et al. which relates to an S I Instruments Brochure, undated. The cell micrograbber is described in the brochure as a hollow metal tube with two tapered tweezer tips of custom design which in a closed position has a thin, stainless steel rod running through the center of it. When the rod is pushed towards the tip using the control box, the fingers of the tip open to allow the tweezers to grasp a muscle fiber. As the stainless steel rod retracts, the tweezers close and hold the fiber. The device is relatively complex to fabricate and operate and has a limited range of utility in terms of force levels.
As will be appreciated from the foregoing, auxotonic, isometric and isotonic force measurement systems have all been employed to measure cell characteristics in various environments, employing various cell attachment mechanisms and devices of various complexity.
Adhesives have also been used to attach single-cell specimens with various attachment methods and devices described in the foregoing references. Silicon, poly-1-lysine, “Great Stuff” by Dow Chemical, and cyanoacrylate glue are known to have been used. With some of these adhesives preparation time is extended because the adhesives require an extended amount of time to set and some can only be used on skinned myocytes. While cyanoacrylate glue sets quickly and provides a strong grip, exposure will kill the cell in a short period of time, leaving a small window of opportunity to test the specimen. Other adhesives are available that are specifically marketed for cell adhesion. These include ECM gel from Sigma-Aldrich, Inc., Matrigel® and Cell-Tak® from BD Biosciences, Inc. Matrigel® and the ECM gel from Sigma-Aldrich are extra-cellular matrices (“ECMs”) derived from Engelbreth-Holm-Swarm mouse sarcoma. Both are too viscous and allow for specimen movement during mechanical testing. Cell-Tak® is a bioadhesive derived from the polyphenolic proteins of marine mussels. More recently, a biocompatible and stronger, more effective and easily processable adhesive was developed and is available through IonOptix (Milton, Mass., Dublin, Ireland). This product is available under the name IonOptix Myotak®. These compositions are described generally in United States Patent Application Publication No. 2012/0034620 of Ward et al.
Despite advances in the art, there exists a pressing need for a more effective cell gripping system which is not destructive or lethal to the cell and allows for measurement of stronger forces applied by or to a live specimen. Simplicity of fabrication and operation are likewise desirable features.